Centrifugal pipe casting method

ABSTRACT

Centrifugal pipe-casting method utilizing a rotatable mold and a permanent-type reusable core for partially closing the mold at its pipe withdrawal end. The portion of the core-facing casting material within the mold presents a surface with indentions for receiving and solidifying casting material so as to hold the end of the pipe and prevent distortion and end-cracking prior to removal of the pipe from the mold.

United States Patent [72] Inventor Jean Denyszyn Lynchburg, Va.

[21] Appl. No. 881,719

[22] Filed Dec. 3, 1969 [23] Division of Ser. No. 639,535, May 18, 1967,

Pat. No. 3,499,479

[45] Patented Oct. 12, 1971 [73] Assignee Glamorgan Pipe & Foundry Co.

[54] CENTRIFUGAL PIPE CASTING METHOD 2 Claims, 4 Drawing Figs.

[52] U.S.Cl 164/114 [51] Int. Cl B22d 13/02 [50] Field of Search 164/66,

[56] References Cited UNITED STATES PATENTS 3,197,827 8/1965 Haughtori164/299 3,327,769 6/1967 Latour 164/286 2,486,870 11/1949 Nolan 164/302X 3,074,130 l/l963 Wittmoser... 164/302 X 3,168,765 2/1965 Bernhardt164/302 Primary Examiner-l Spencer Overholser Assistant Examiner.lohn S,Brown Attorney-Shanley and O'Neil ABSTRACT: Centrifugal pipe-castingmethod utilizing a rotatable mold and a permanent-type reusable core forpartially closing the mold at its pipe withdrawal end. The portion ofthe core-facing casting material within the mold presents a surface withindentions for receiving and solidifying casting material so as to holdthe end of the pipe and prevent distortion and end-cracking prior toremoval of the pipe from the mold.

PATENTEU 0211 21am FIG] CORE

I IIIIIIII T N E M F. V 0 M L AW W W3 TM 66 m L w" 6 2 CENTRIFUGAL LOSUPPORT CENTRIFUGAL L COVER PLATE FIG. 2

INVENTOR JEAN DENYSZYN CQ ATTO CENTRIFUGAL PIPE CASTING METHOD Thisapplication is a division of application Ser. No. 639,535, now US. Pat.No. 3,499,479 entitled Centrifugal Pipe-Casting Apparatus", filed May18, 1967 by Jean Denyszyn.

This invention is concerned with centrifugal casting of pipe. In itsmore specific aspects, the invention is concerned with a permanent-typecore which can be used repeatedly with centrifugal casting apparatus inthe formation of no-hub pipe.

In the centrifugal casting of iron pipe, a controlled amount of molteniron is fed into a rotating elongated mold which moves longitudinallyduring casting to form a pipe. The rotating mold is a pennanent orsemipermanent structure which must be open at one end for withdrawal ofthe cast pipe. During casting, that end of the rotating mold must bepartially closed with a core to form what is commonly referred to as thebell end of the pipe and retain metal in the mold for the entirecasting. Such cores must be readily removable upon completion of eachcast.

To a large extent, the art has relied on use of expendabletype sandcores which are friable and can be removed from the mold and the pipeupon completion of each cast. The manufacture of such sand cores, thecareful handling required with cores, the removal of sand from the castpipe, and other such problems increase the cost of manufacturing castpipe using sand cores. It is also difficult to manufacture uniform,symmetrical sand cores which will consistently fit the pipe withdrawalend of a rotating mold and provide crack and distortion-free pipe ends.In practice cracks are ordinarily formed in the pipe ends by metal whichruns between the mold and the sand core. This metal forms fins on thepipe which,

due to rapid cooling, generate cracks which are propagated into thepipe.

An object of the present invention is to provide casting apparatus ableto withstand continuous rugged use and semiautomated functioning with aminimum of attention by working personnel. Also to provide castingmethods which will consistently produce uniform product which does notneed trimming, cleaning, or machining to be within requiredspecifications. To meet these requirements a permanent-type metalliccore which can be accurately and quickly fitted to a rotatable mold isprovided. Further, a metallic core is provided which is adaptable foruse with self-locking mechanisms for rotatable molds.

However, it has been found that merely substituting metallic cores forsand cores does not provide the yield and economies required forcommercial production. Many of the difficulties encountered are believedto stem, at least in part, from toorapid chilling of molten metalcontacting a metallic core. This rapid chilling of the metal at the bellend of the pipe is believed to be the cause of the distortion produced,for example an elliptical shape occurs at the pipe withdrawal end of thepipe rather than the desired circular configuration. Cracking of thepipe at the pipe withdrawal end as a result of this distortion orbecause of fin formation also decreases the yield. Distortion and endcracking caused by metallic cores have been found to decrease yield inexcess of twenty percent so that it has not been economically possible,prior to the present invention, to replace sand cores with permanenttypecores.

It is the primary objective of the present invention to provide apermanent-type core, which circumvents the abovedescribed pipe-castingproblems, which uniformly produces crack-free and distortion-free pipe,and which can be used repeatedly, notwithstanding rough handling andextreme thermal stresses.

Referring to the accompanying drawings:

FIG. 1 is a schematic view of centrifugal casting apparatus,

FIG. 2 is a cross-sectional view of portion of a rotatable mold castingapparatus and a permanent-type core embodying the present invention,

FIG. 3 is an end view of a portion of permanent-type core embodying thepresent invention, and

FIG. 4 is a sectional view of a portion of the core of FIG. 3.

In operation of the apparatus shown in FIG. 1, molten metal iscontrollably fed for each casting operation from pouring box 12 to theinterior of rotatable mold 141 through spout 16. At the beginning of thecast spout 16 extends about half the length of the mold toward its bellend. Rotatable mold 14 is spun about longitudinal axis 18 during eachcasting operation.

Prior 'to casting, core 20 is fitted to the rotatable mold 14. At thestart of casting, metal from spout 16 contacts facing 22 of core 20. Themetal is fed at such a rate, and the rotatable mold moves longitudinally(as indicated by arrow 26) at such a rate that a substantially uniformthickness pipe 24 is formed. Casting machines using a rotatablelongitudinally moving mold, e.g. Delavaud centrifugal pipe-ca5tingmachines, are well known in the art and no further explanation of thegeneral principle of operation is required for an understanding of theinvention. The removable core problems discussed above are also wellknown in the art and have constrained these semiautomatic machines touse of sand cores for many years.

FIG. 2 shows the permanent-type core of the present invention andportions of a rotatable mold along with self-locking structure. Core 28is substantially symmetrical about longitudinal axis 30 and has anelongated hollow tubular configuration. The hollow portion of core 28 isin communication with the hollow tubular internal cavity of mold 34. Theinterior surface of core 28 is generally smooth and curvilinear defininga portion of a conical surface. The exterior surface of core body 32,which includes shoulder 33, has a configuration adapted for functioningof centrifugally operated self-locking fingers such as that shown at 36.Rotation of the mold provides the force for functioning of theself-locking mechanism. Other suitable locking mechanisms may be used inpractice of the invention.

Core 28 is removably secured to rotatable pipe mold 34 and presents apatterned surface to a portion of the hollow tubular internal cavitydefined by rotatable pipe mold 34. The patterned surface of one end ofmold 28 closes a portion of the hollow internal cavity of rotatable mold34 contiguous to the internal periphery of the mold determining theminimum internal diameter of the pipe. The patterned surface presentedby core 28 contact molten metal poured into the mold and establishingthe mold surface for the pipe end wall.

Contact of molten metal with a metallic core is believed to have beenresponsible for the problems experienced before the present invention.Rapid chilling of the casting metal where contact was made with thecore, and the differential chilling of metal contacting the core andmetal contacting the mold, caused distortion of the pipe at itswithdrawal end. An elliptical configuration at the withdrawal end of thecast pipe resulted rather than the desired circular configuration.Normally the ellipticalness extended several inches along the length ofthe pipe. As a result, either the entire pipe was scrapped or someportion of the pipe had to be cut off in order to salvage a pipe withlimited uses, so that commercially acceptable yield could not beobtained.

The present invention solved these difficulties be devising means forholding metal at the withdrawal end of the pipe during the casting andpipe-forming stages to prevent shrinkage, distortion, and cracking atthe pipe end.

In practice, the core body configuration of the present invention canvary widely to suit the type of lock design employed. However, acore-facing insert 40 is positioned at the end of core 28 contacting therotatable mold 34. Diametral dimensions of core-facing insert 40 areselected to maintain the pipe ends within thickness requirements. Thefacing insert 40 fits firmly into the mold to keep molten metal frombetween the core and the mold. That ortion of core-facing insert 40which comes into direct contact with the molten metal is manufacturedwith recesses for receiving and solidifying casting metal so as to holdthe end of the pipe at the pipe withdrawal end of the rotatable moldagainst radial shrinkage forces during casting of the remainder of thepipe and until the pipe is removed from the mold.

Recesses in the core-facing insert 40 can vary in shape, depth andnumber depending on the type of metal being cast and the size pipc beingcast. They can be formed in core-facing insert 40 by various meansincluding drilling and knurling.

In the embodiment shown in FIGS. 3 and 4 a plurality of indentations,such as 44, are used. These indentations can be distributed uniformlyabout core-facing insert 46 in order to provide uniform gripping of themetal. Preferably the outer configuration of the indentations iscurvilinear in order to avoid opportunity for forming minor cracks atthe end surface of the pipe.

The depth of the indentations can vary depending on the diameter of thepipe being cast and the type of metal being cast. A depth of about onethirty-second inch has been found satisfactory for standard cast ironpipe. The depth of the indentations should be sufficient to hold thepipe against radial shrinkage forces. However, the depth of theindentations should not cause difficulty in removing the core or requireremoval of protrusions formed in the end surface of the pipe by themetal which is cast in the indentations.

The number of indentations can also vary with the size of the pipe. In arepresentative embodiment of the invention for casting 4-inch diameterpipe, 30 indentations of outer diameter, one thirty-second inch depth,and a conical configuration as shown in FIG. 4 have been found to besatisfactory. With a 3-inch diameter pipe, 24 such indentations havebeen found to be satisfactory.

Considering useful life of a core, unexpected results are obtained byusing brass for the core facing means. This longer life is believed tostem from the better thermal conductivity of the brass than thatavailable with other suitable metals such as stainless steel. inpractice a brass facing means about A in thickness, with recess means asabove described, is welded to the core body. Suitable core body metal isductile iron. This combination has resulted in long useful life, inexcess of 5,000 casts per core, notwithstanding the thermal shockencountered when the core is immersed in water after each casting.

Suitable metals for the core-facing means include stainless steel,steel, iron, etc. Also satisfactory operation can be obtained by castingthe entire core from a metal such as ductile iron and preparing theabovc-described pattern in the face which contacts the molten metal.However, a brass core-facing means and ductile iron core body combinesfeatures which make the core perform satisfactorily during each cast andrugged enough to withstand thousands of casts.

Alternate heating of the core during casting and cooling by quenching inwater immediately after casting cause thermal fatigue which eventuallydetermines the life of the core. This can be circumvented by eliminatingthe quenching step, but advantages, such as ease of handling of the coreby the operator after quenching, making the quenching practice moresuitable economically.

The present invention eliminates the problem of ellipticalness and endcracking in centrifugal pipe casting and provides permanent-typeapparatus able to withstand the rugged use and thermal stressesencountered. As a result, the yield and quality of the product, andproduction rate of centrifugal casting apparatus, are increased.Specific structure and materials have been set forth in disclosing theinvention. However, the scope of the invention is not limited to suchdisclosure but rather is to be determined from the appended claims.

What is claimed is:

ll. Method for centrifugal casting of no-hub pipe using a reusable-typemetallic core removably secured to a rotatable mold having an internalsurface for molding molten metallic casting material and having a pipewithdrawal end, comprising the steps of controllably feeding moltenmetallic casting material into the mold with the reusable-type metalliccore positioned at the pipe withdrawal end of the mold presenting apatterned surface sealing a portion of the mold contiguous to itsinternal surface to determine the minimum internal diameter of the pipebeing cast and establish a mold surface for the end wall of such piperotating the mold during controlled feeding of molten metallic castingmaterial to the mold, and

solidifying molten metallic casting material at the pipe withdrawal endof the mold prior to solidification of the remainder of the pipe whileavoiding pumping of such material with the patterned surface of themetallic core establishing a pattern in the pipe end wall and holdingthe pipe at the pipe withdrawal end of the mold so as to preventshrinkage distortion at that end of the pipe during casting andsolidification of the remainder of the pipe.

2. In the centrifugal casting of no-hub pipe, a method for preventingradial shrinkage of the pipe at the pipe withdrawal end of the mold whenusing a reusable-type metallic core for partially closing that end ofthe mold along its inner periphery, comprising the steps of controllablyfeeding casting metal to the rotatable mold,

rotating the mold about its longitudinal axis and moving the moldlongitudinally to distribute the metal being controllably fed into themold, and

presenting a patterned surface of the metallic core for establishing theminimum internal diameter for the pipe being cast and defining a moldsurface for the end wall of such pipe, such patterned surface being intransverse relationship to the longitudinal axis of the mold andpositioned along the inner periphery of the rotatable mold to receiveand solidify molten casting material prior to solidification of theremainder of the pipe so as to hold the pipe at the pipe withdrawal endof the mold during casting and solidification of the remainder of thepipe while avoiding pumping of such molten casting material.

1. Method for centrifugal casting of no-hub pipe using a reusable-typemetallic core removably secured to a rotatable mold having an internalsurface for molding molten metallic casting material and having a pipewithdrawal end, comprising the steps of controllably feeding moltenmetallic casting material into the mold with the reusable-type metalliccore positioned at the pipe withdrawal end of the mold presenting apatterned surface sealing a portion of the mold contiguous to itsinternal surface to determine the minimum internal diameter of the pipebeing cast and establish a mold surface for the end wall of such pipe,rotating the mold during controlled feeding of molten metallic castingmaterial to the mold, and solidifying molten metallic casting materialat the pipe withdrawal end of the mold prior to solidification of theremainder of the pipe while avoiding pumping of such material with thepatterned surface of the metallic core establishing a pattern in thepipe end wall and holding the pipe at the pipe withdrawal end of themold so as to prevent shrinkage distortion at that end of the pipeduring casting and solidification of the remainder of the pipe.
 2. Inthe centrifugal casting of no-hub pipe, a method for preventing radialshrinkage of the pipe at the pipe withdrawal end of the mold when usinga reusable-type metallic core for partially closing that end of the moldalong its inner periphery, comprising the steps of controllably feedingcasting metal to the rotatable mold, rotating the mold about itslongitudinal axis and moving the mold longitudinally to distribute themetal being controllably fed into the mold, and presenting a patternedsurface of the metallic core for establishing the minimum internaldiameter for the pipe being cast and defining a mold surface for the endwall of such pipe, such patterned surface being in transverserelationship to the longitudinal axis of the mold and positioned alongthe inner periphery of the rotatable mold to receive and solidify moltencasting material prior to solidification of the remainder of the pipe soas to hold the pipe at the pipe withdrawal end of the mold duringcasting and solidification of the remainder of the pipe while avoidingpumping of such molten casting material.